The present disclosure relates to methods and compositions for use in drilling operations. Particularly, the present disclosure is directed toward tagged detectable additives for use in drilling fluids and methods of detection and quantification thereof.
Many subterranean operations involve the drilling of a well bore from the surface through rock and/or soil to penetrate a subterranean formation containing fluids that are desirable for production. In the course of drilling operations and other subterranean operations, the drill string and/or other equipment may contact zones of rock and/or soil containing tar (e.g., heavy hydrocarbons, heavy oil, asphalt, bitumens, and the like); in many such operations, it may be desirable to drill the well bore through these tar-containing zones. However, tar is a relatively tacky substance that may readily adhere to surfaces that it contacts, including the surfaces of the well bore and/or any equipment utilized therein.
Tar also may dissolve into many synthetic treatment fluids used in the course of drilling operations, increasing the tacky and adhesive properties of the tar and affecting the rheological profile of the treatment fluid. If a sufficient amount of tar dissolves into the treatment fluid, the tar may contact and adhere to surfaces of equipment used in the well bore or the well bore itself. This may, among other problems, prevent the drill string from rotating, prevent fluid circulation, or otherwise impede the effectiveness of a drilling operation. In some cases, it may become necessary to remove and/or disassemble the drill string in order to remove accretions of tar, a process that may create numerous cost and safety concerns. The accretion of tar on drilling equipment and/or in the well bore also can impede any subsequent operations, including cementing, acidizing, fracturing, sand control, and remedial treatments. In addition, soft, tacky tar that manages to reach the surface may foul surface equipment, including solids screening equipment.
Existing methods of managing these tar incursion problems may be problematic. Some of these methods involve affecting an increase in hydrostatic pressure in the well bore so as to force the tar out of the well bore to the surface. However, this increased hydrostatic pressure may damage the well bore and/or a portion of the subterranean formation.
Other conventional methods utilize treatment fluids that comprise dispersants, surfactants, and/or solubilizers, which allow the tar particles to dissolve in or homogenize with the treatment fluids. However, the tar particles may not be readily separated out of the fluid once they have dissolved into or homogenized with the fluid. The presence of the tar particles in the treatment fluid may alter its rheological properties and/or suspension capacity, which may limit its use in subsequent operations. Moreover, the addition of these dispersants, surfactants, and solubilizers may increase the complexity and cost of the drilling operation.
Polymers, both natural and synthetic, are utilized in the drilling and completion of subterranean wells in a variety of functions, such as components of treatment fluids to overcome the aforementioned tar accretion problem. These treatment fluids may comprise an aqueous fluid and a polymer. As used herein, the term “treatment fluid” refers to any fluid that may be used in a subterranean application in conjunction with a desired function and/or for a desired purpose. The term “treatment fluid” does not imply any particular action by the fluid or any component thereof. A polymeric material may be ionic or nonionic in nature. The polymers may interact with the tar resident in a well bore such that the properties of the tar are altered. Optionally, the polymer may bind or coat the tar such that the tar becomes less sticky. Thus, the polymer(s) should be added to the well bore in a quantity sufficient to treat the tar therein.
However, as the polymers are utilized during drilling operations, the amount of polymers is diminished. When the level of polymer in the treatment fluid gets below a certain concentration, the ability of the polymer to perform its intended task is significantly reduced. As such, the ability of ascertaining the concentration of a polymer in a sample of drilling or completion fluid is highly valuable, but often relies on advanced techniques, such as gas chromatography (GC), mass spectroscopy (MS), pyrolysis GC/MS, and the like, which may be unsuitable for application in the field and may not provide real-time data. Samples usually have to be taken away from a well site in order to be tested by such techniques, and then the data returned to the well. In other conventional drilling, drilling operators simply add more polymers to the drilling fluid without actually knowing the amount of polymers remaining in the drilling fluid. This could cause waste of the polymer leading to higher costs of drilling.
Even if suitable techniques for detecting the polymer could be used at the well site, interference resulting from the large number of additives present in drilling and completion fluids, as well as potential interferences from formation fluids, may make these techniques seemingly unsuitable in the field. These interferences may show absorbance/emission bands that overlap with the absorbance/emission bands of the polymers under study. This is particularly true in the ultraviolet region of the electromagnetic spectrum, which is otherwise a very rich region for concentration determination. Despite these limitations, the ease and reliability of a spectrometric method is still thought to be highly desirable for field quantification of polymer concentration.